Toxins In Urban Food Gardens?

While I have only just glanced at this subject, picking up the warning from an 'Eat The Weeds' episode on You Tube, it certainly seems like yet something else to seriously consider when thinking about urban food gardens:

Two examples:

"Conclusions

...Particularly in urban and industrialized areas, environmentally based contamination in locally grown food complicates any prospect of regional food autonomy. The 100-year history of urban allotment agriculture in Poland provides a prototype of an urban-based food system, as well as a warning. Addressing the issues of food safety and respect for the need for local food production requires a redefinition of local food sustainability..."

"Empirical evidence from the city of Kano in northern Nigeria suggests that there is currently much reason for concern as industrial and domestic toxins are reaching dangerously high levels. As soils and water channels become increasingly polluted, the sustainability of urban and peri-urban food production is questioned. Since the health implications of long-term exposure to toxins are unclear, it is suggested that coordinated longitudinal research involving urban planners, agricultural scientists and health specialists is urgently needed."